There are variety of microfluidic devices which are useful in a variety of applications, including for performing chemical, clinical, and environmental analysis of chemical and biological samples. Microfluidic devices are often fabricated using photolithography, wet chemical etching, and other techniques similar to those employed in the semiconductor industry. The resulting devices can be used to perform a variety of sophisticated chemical and biological synthetic and analytical techniques.
Microfluidic devices are particularly well suited for microscale chemical synthesis and analysis of minute quantities of samples. The amount of sample required is typically on the order of nanoliters and even picoliters. Microfluidic devices can be produced at relatively low cost, and the channels can be arranged to perform numerous specific analytical or synthetic operations, including mixing, dispensing, valving (i.e., controlling the flow of samples), detecting, conducting electrophoresis, and the like. The synthetic and analytical capabilities of microfluidic devices are generally enhanced by increasing the number and complexity of network channels, reaction chambers, and the like.
Unfortunately, the structures and methods used to introduce samples and other fluids into microfluidic devices can limit their capabilities. Fluid introduction ports (i.e., orifices or fluid inlets/outlets) provide an interface between the surrounding world and the microfluidic channel network. Current structures and methods for transporting fluids to and from microfluidic devices generally result in the transfer of a much greater volume of fluid than is needed for microfluidic synthesis or analysis.
Recently, microfluidic devices fabricated from elastic materials have been developed providing a variety of sample manipulations within the microfluidic devices, thereby significantly increasing the utility of microfluidic devices. For example, such microfluidic devices have been demonstrated to be useful in combinatorial synthesis, and sorting minute particles, cells, oligonucleotides, peptides, and other detectable molecules. However, one problem that remains is introduction of samples into the microfluidic devices. Although the capacity of most microfluidic devices is in the order of nanoliters or picoliters, typically a sample on the order of microliters is required for transfer into microfluidic devices. This relatively large quantity of sample needed negates one of the primary advantages of using microfluidic devices in sample analysis and synthesis.
Similarly, there have been few methods developed for transferring small quantities of sample from microfluidic devices to conventional fluid handling systems. One of the primary method uses electroosmotic forces which requires ionic solutions to transport fluids to and from or within the microfluidic channel. This requirement of having ionic solution to transport a fluid medium also severely limits the applicability of microfluidic devices.
Therefore there is a need for microfluidic devices or systems which facilitate the transfer of small volumes (i.e., in the order of less than about 1 μL, and preferably less than 0.1 μL) of samples or fluids to and from the microfluidic devices. There is also a need to increase the number of fluids which can be manipulated within the microfluidic device without increasing the overall size of the microfluidic device itself. There is also a need for providing a means for filling or dispensing a predetermined amount of samples or fluids to and from the microfluidic channels.